Although the present disclosure has applicability beyond automotive, an automotive example and discussion is herein provided for context only, and to specifically demonstrate at least one potential area of its utility.
Accordingly, an automotive vehicle includes an internal combustion engine containing a rotary crankshaft configured to transfer motive power from the engine through a driveshaft to turn the wheels. A transmission is typically interposed between engine and driveshaft components to selectively control torque and speed ratios between the crankshaft and driveshaft. In a manually operated transmission, a corresponding manually operated clutch may be interposed between the engine and transmission to selectively engage and disengage the crankshaft from the driveshaft to facilitate manual shifting among available transmission gear ratios.
On the other hand, if the transmission is automatic, the transmission will normally include an internal plurality of automatically actuated clutches adapted to dynamically shift among variously available gear ratios without requiring driver intervention. Pluralities of the clutches, also called clutch modules, are incorporated within such transmissions to facilitate the automatic gear ratio changes.
In an automatic transmission of an automobile, multiple gear ratios are generally available, not including a reverse gear. The various gears may be structurally comprised of inner gears, intermediate gears such as planet or pinion gears supported by carriers, and outer ring gears. Specific transmission clutch modules may be associated with specific sets of the selectable gears within the transmission to facilitate the desired ratio changes.
For example, one of the clutch modules of an automatic transmission associated with first (low) and reverse gear ratios may be normally situated at the front of the transmission and closely adjacent the engine crankshaft. The clutch may have an inner race and an outer race disposed circumferentially about the inner race. One of the races, for example the inner race, may be drivingly rotatable in only one direction. The inner race may be selectively locked to the outer race via an engagement mechanism such as, but not limited to, a roller, a sprag, or a pawl, as examples. In the one direction, the inner race may be effective to directly transfer rotational motion from the engine to the driveline.
Within the latter system, the outer race may be fixed to an internal case or housing of an associated planetary member of the automatic transmission. Under such circumstances, in a first configuration the inner race may need to be adapted to drive in one rotational direction, but freewheel in the opposite direction, in a condition referred to as overrunning. Those skilled in the art will appreciate that overrunning may be particularly desirable under certain operating states, as for example when a vehicle is traveling downhill. Under such circumstance, a driveline may occasionally have a tendency to rotate faster than its associated engine crankshaft. Providing for the inner race to overrun the outer race may act to reduce drag and/or spin losses, for example.
In a second configuration, such as when a vehicle may be in reverse gear, the engagement mechanisms may be adapted for actively engaging in both rotational directions of the inner race, thus not allowing for the overrunning condition in the non-driving direction.
In yet other configurations, a clutch module may switch between modes adapted to be locked in another direction of rotation in a third mode, and to freewheel in both directions of rotation in an alternate, or fourth, mode.
A significant issue has been related to actuators designed and adapted to switch clutch modules between their operative modes. Most such actuators have been bulky add-on, or adjunct, apparatus adapted to interact with the clutch module from outside of a generally circumferential envelope of the module, per se. As industry pressures have increasingly mandated reductions in footprints and/or sizes of automotive parts, improved actuators having such reduced footprints are needed.